This invention relates generally to methods and systems for controlling the partial pressure of air in an intake manifold of an engine.
As is known in the art, the mass of air, or cylinder air charge, inducted into each cylinder of an internal combustion engine must be known as precisely as possible in order to match the air mass with an appropriate mass of metered fuel. Placing sensors at the intake port of each cylinder is technically very difficult and expensive. Instead, a sensor is typically located either inside the intake manifold or at the throttle opening into the intake manifold. A physics model is then used to estimate the air mass propagation through the intake manifold into each cylinder.
Two types of the above-described sensors are typically employed in internal combustion engines. One type is a manifold absolute pressure (MAP) sensor. An estimation algorithm treats the manifold pressure as an input to the system and uses mapped engine data and engine speed to estimate air flow into the engine cylinders. The other type of sensor is a relatively expensive mass air flow (MAF) sensor used to directly measure mass air flow at the throttle body. For the MAF based system, fresh air from the throttle is directly measured. EGR gas content is left out of the cylinder port air charge estimation. Other air flows not from the throttle (via vacuum lines from the brakes, canister purge system, etc.) are not accounted for by the MAF measurement and must be accounted for by other means.
The MAP sensor measures the absolute pressure in the intake manifold and thus incorporates the air flow from all sources. Difficulties arise, however, when gases other than air are introduced into the intake manifold. For the MAP based system (often referred to as a speed density system), gases other than air, such as the deliberately introduced exhaust gas (referred to as EGR or exhaust gas recirculation), increase the manifold pressure. These gases should not be matched by fuel. However, the MAP sensor cannot distinguish between fresh air and EGR. Thus, EGR mass in the intake manifold must be measured or estimated.
More particularly, control of the partial pressure of air has to be achieved under uncertainties in the EGR flow. These uncertainties are due to the soot deposits in the EGR valve conduit and the fact that the exhaust pressure and temperature are not measured. Additionally, air is present in the EGR flow during lean operation and this air needs to be accounted for in the partial pressure of air estimate.
In accordance with the present invention, a method is provided for controlling partial pressure of air in an intake manifold of an engine. The engine has an intake throttle device for controlling a flow of air to the intake manifold. An EGR valve is provided for controlling a flow of exhaust gas from the engine to the intake manifold downstream of the intake throttle. The engine has at least one cylinder fed a flow comprising air passing through the throttle to the intake manifold and exhaust products passing through the EGR valve to the intake manifold. Both the air through the throttle and the exhaust gas products in the intake manifold are passed as a combined flow to the intake manifold and then to the at least one cylinder. The method includes: specifying a dynamic reference model for the desired partial pressure of the air as a function of time; and controlling the flow through the intake throttle device in accordance with an estimated EGR flow obtained by a dynamic observer and an estimate of partial air fraction in the exhaust gas products.
In one embodiment, the partial air fraction is estimated in accordance with intake to exhaust delay and fuel injection to exhaust delay.
In one embodiment the dynamic observer does not require information of engine exhaust temperature, engine exhaust pressure, or EGR valve position.
According to the present invention, there is provided a method controlling partial air pressure in an intake manifold of an engine. The engine has an intake throttle device for controlling a flow of air to the intake manifold. An EGR valve is provided for controlling a flow of exhaust gas from the engine to the intake manifold downstream of the intake throttle. The engine has at least one cylinder fed a flow comprising air passing through the throttle to the intake manifold and exhaust products passing through the EGR valve to the intake manifold. Both the air through the throttle and the exhaust gas products in the intake manifold are passed as a combined flow to the intake manifold and then to the at least one cylinder. The method includes: calculating the desired partial pressure of air dynamically, as a function of time in accordance with a reference model, estimating the flow of exhaust gas products passing through the EGR valve to the intake manifold from engine operating parameters; estimating the air fraction in the estimated flow of exhaust gas products passing through the EGR valve to the intake manifold; determining the partial pressure of air in the intake manifold from such estimate of the flow of exhaust gas products and such estimate of the air fraction; and, adjusting the intake throttle device in accordance with a difference between a desired partial pressure of the air in the intake manifold and the determined partial pressure of air in the intake manifold.
In a preferred embodiment of the invention, the estimate of the flow of gas products passing through the EGR valve comprises providing such estimate in accordance with an open loop estimator.
In accordance with the present invention, a method is provided for controlling partial air pressure in an intake manifold of an engine. The method includes estimating partial air pressure in intake manifold based on open loop observer and estimated partial air fraction in the flow of exhaust to the intake manifold.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.